The present invention relates generally to electronic communication systems, and in particular, to systems and methods for transmitting and receiving information from such systems over a computer network.
With the increasing popularity of the Internet and other content-heavy electronic communication systems, there has been a substantial need for reliable and affordable high bandwidth mediums for facilitating data transmissions between service providers and their customers. In relation to the requirement that such mediums be affordable to consumers, it was determined that the most cost-effective manner for providing service to customers was by using infrastructure already present in most locations. Accordingly, over recent years, the two such mediums most widely meeting these requirements include the cable television (CATV) and the conventional copper wire telephone systems (plain old telephone system or POTS).
Relating specifically to the adaptation of POTS telephone lines to carry data at high-bandwidth or ‘broadband’ data rates, a number of Digital Subscriber Line (DSL) standards and protocols have been proposed. DSL essentially operates by formatting signals using various Time Domain Equalization techniques to send packets over copper wire at high data rates. A substandard of conventional DSL is known as Asymmetric Digital Subscriber Line (ADSL) and is considered advantageous for its ability to provide very high data rates in the downstream (i.e., from service provider to the user) direction by sacrificing speed in the upstream direction. Consequently, end user costs are minimized by providing higher speeds in the most commonly used direction. Further, ADSL provides a system that applies signals over a single twisted-wire pair that simultaneously supports (POTS) service as well as high-speed duplex (simultaneous two-way) digital data services.
Two of the proposed standards for ADSL are set forth by the International Telecommunications Union, Telecommunication Standardization Section (ITU-T). A first, conventional, ADSL standard is described in ITU-T Recommendation G.992.1—“Asymmetric Digital Subscriber Line (ADSL) Transceivers”. A second, G.992.3, ADSL2 is a new standard recently completed and approved by the International Telecommunications Union (ITU) in 2002 that will supersede existing ADSL standards. Work being done under the headings of “G.dmt.bis” and “G.lite.bis” is nearing completion to designate G.992.3 and G.992.4 for full-rate ADSL and splitterless ADSL, respectively. Much has been learned over the past three years of ADSL deployments, including areas where improvements in the technology would be particularly valuable. There is a wide variety of improvements included in ADSL2, each with very different implications; some make the transceivers operate more efficiently, some make them more affordable, and some add functionality.
As briefly described above, all DSL system operate in essentially the following manner. Initial digital data to be transmitted over the network is formed into a plurality of multiplexed data frames and encoded using special digital modems into analog signals which may be transmitted over conventional copper wires at data rates significantly higher than voice band traffic (e.g., ˜1.5 Mbps (megabits per second) for downstream traffic, ˜150 kbps (kilobits per second) for upstream traffic). The length and characteristics of wire run from a customer's remote transceiver to a central office transceiver may vary greatly from user to user and, consequently, the possible data rates for each user also vary. In addition, the physical channel (i.e., the wires themselves) over which the system communicates also vary over time due to, for example, temperature and humidity changes, fluctuating cross-talk interference sources. The distribution of signal energy over frequency is known as the power spectral density (PSD). Power spectral density is simply the average noise power unit of bandwidth (i.e. dBm/Hz). All transmission systems have a finite power and bandwidth and, therefore, the power and bandwidth of each system is used in a manner so as not to disturb other adjoining systems. A PSD mask is used which is defined as the maximum allowable PSD for a service in presence of any interference combination. The transmit spectrum for a service refers to the PSD of the transmitted signal. Spectral compatibility of the system using a modem boosted modes for improved modem rates and extended reach solutions into existing services may either be without distance limitations or partially limited distance when the spectral compatibility impact is higher than the existing service disturbance beyond a specific reach. The choice between limited and unlimited distance boosted modes are done at the network management level which requires a costly procedure from the telephone company (Telco) to provide physical layer information that also covers how the existing services are deployed, and because of the costs involved, broadband services providers shy away from all the boosted mode solutions, specially the limited distance boosted modes, thereby, restraining the coverage and performance of the underlying service deployment.